As a core technology of a next-generation transport network, an OTN (Optical transport network) includes electric-layer and optical-layer technical specifications, features diverse OAM (Operation, Administration and Maintenance,), and is capable of powerful TCM (Tandem Connection Monitoring) and outband FEC (Forward Error Correction), allowing flexible scheduling and management for large-capacity services.
On an electric processing layer, the OTN technology defines a standard encapsulation structure, which maps various client services, and can implement management and monitoring for client signals. An OTN frame structure is shown in FIG. 1, the OTN frame is a structure of 4×4080 bytes, that is, 4 rows×4080 columns. The OTN frame structure includes a frame delimiting area, OTUk (Optical Channel Transport Unit) OH (Overhead), ODUk (Optical Channel Data Unit) OH, OPUk (Optical Channel Payload Unit) OH, an OPUk payload area (Payload Area), and a FEC area, where values 1, 2, 3, and 4 of k correspond to rate levels 2.5 G, 10 G, 40 G, and 100 G respectively. The frame delimiting area includes an FAS (Frame Alignment Signal) and an MFAS (Multi-frame Alignment Signal), information in the OPUk OH is primarily used for mapping and adaptation management of a client service, information in the ODUk OH is primarily used for managing and monitoring an OTN frame, and information in the OTUk OH is primarily used for monitoring a transmission section. A fixed rate of the OTUk is called a line interface rate. Currently, line interface rates of four fixed rate levels 2.5 G, 10 G, 40 G, and 100 G exist. The OTN transmits a client signal in the following manner: mapping an upper-layer client signal to an OPUj of a lower rate level and adding OPUj overhead and ODUj overhead to form an ODUj, which is herein called a lower-order ODUj; and then mapping the lower-order ODUj to an OPUk of a higher rate level, and adding OPUk overhead, ODUk overhead, OTUk overhead, and a FEC to form a constant-rate OTUk, where the OTUk is called a higher-order OTUk; and modulating the higher-order OTUk onto a single optical carrier for transmission, where a bearer bandwidth of the optical carrier is equal to a fixed rate of the higher-order OTUk. In addition, an ODUflex is introduced in an existing OTN, and is called a lower-order variable-rate optical channel data unit, and is used to carry an upper-layer service of any rate. The lower-order ODUflex needs to be mapped to the higher-order OPUk first, and the OPUk overhead, the ODUk overhead, the OTUk overhead, and the FEC are added to form a constant-rate higher-order OTUk, and then the higher-order OTUk is modulated onto a single optical carrier for transmission.
Massive increase and flexible change of upper-layer client IP (Internet Protocol) services impose challenges to an optical transport network system. Currently, optical spectrum resources are divided according to 50 GHz optical spectrum grid bandwidths, and a 50 GHz optical spectrum grid bandwidth is allocated to each optical carrier. For optical carriers whose bearer bandwidths fall within the four fixed rate levels 2.5 G, 10 G, 40 G, and 100 G, optical spectrum width occupied by the optical carriers does not reach 50 GHz, and waste of optical spectrum resources exists. Moreover, the optical spectrum is a limited resource. To make full use of optical spectrum resources, improve overall transmission capabilities of a network, and fulfill increasing upper-layer client IP (Internet Protocol, protocol for interconnection between networks) service transmission, a Flex Grid (flexible grid) technology is introduced into an optical layer to extend the optical spectrum grid bandwidth division of the optical spectrum resources from a constant 50 GHz granularity (ITU-T (International Telecommunication Union—Telecommunication Standardization Sector-telecommunication) G.694) to optical spectrum grid bandwidth division of a smaller granularity. Currently, a minimum optical spectrum grid bandwidth granularity is slot=12.5 GHz, and an optical carrier can occupy one or more continuous optical spectrum grid bandwidths. The OTN network may allocate a proper optical spectrum width according to a traffic volume of a client signal to be transmitted and a transmission distance, so as to meet transmission requirements.
In addition, persons in the art expect to increase spectrum efficiency as far as possible. To obtain higher spectrum efficiency, higher-order modulation is required, such as nQAM (n-order quadrature amplitude modulation) and an orthogonal frequency division multiplexing (OFDM, Orthogonal Frequency Division Multiplexing) technologies. That is, under a constant spectrum width, actual traffic volume requirements are fulfilled by changing an optical carrier modulation format.
However, currently an electric-layer OTN line interface has a fixed rate level, and it is not practicable to provide a line interface of a proper rate according to the actual traffic volume of the client service, and therefore, optimal configuration of optical transport network bandwidth resources is not available.